The present invention relates to a technique for processing an object to be treated in a plurality of processes and more particularly to a technique for processing semiconductor wafers.
Semiconductor integrated circuit devices, such as logic ICs, memory ICs and one-chip microcomputers, are fabricated by forming semiconductor circuit elements into a silicon wafer through diffusion, wiring and other processes and dividing the wafer into single semiconductor integrated circuit devices (individual semiconductor chips).
The wafer manufacturing process to build semiconductor circuit elements into a semiconductor wafer basically comprises: a cleaning process to clean the surface of the wafer; an oxidation process to form a uniform oxidized film over the wafer surface; a diffusion process to diffuse impurity atoms into the silicon substrate; and a photo-etching process that, after transferring a desired device pattern onto the photoresist, performs an etch on the photoresist to form a target pattern. These processes are repetitively performed on the semiconductor wafer a number of times.
To manufacture a semiconductor integrated circuit device based on a circuit pattern whose design was completed in the previous step, apparatuses that perform the above-mentioned processes, such as a cleaning equipment, an oxidation equipment, a low-pressure CVD equipment, and a photo-etching equipment, are constructed in the same way as in the actual production line. Then, a sample or experimental product of the semiconductor wafer is made by using the production line thus set up and is subjected to tests such as a circuit operation test to check the sample wafer, followed by the mass production of the semiconductor wafer. If the tests have found that the prepared production line cannot produce a desired product, the conditions of each process are adjusted and another sample is manufactured.
In building the production line, it is preferred to set the layout of each process so that the processing time of each process for one wafer is almost equal. In the low-pressure CVD equipment used in the production line, for example, 100 wafers are processed in a batch, which takes about four hours. Hence, the processing time for one wafer is about 2 and a half minutes.
In the photolithography apparatus that transfers a device pattern onto the photoresist, about 25 wafers are set in the apparatus and processed one at a time. The processing time for each wafer is about 2-3 minutes.
To fabricate a sample wafer, the steps involve, as mentioned above, first setting up a production line, operating the production line under the same condition as when manufacturing the actual production type wafer, and then inspecting the sample. Thus, the inspection can be made of the sample wafer if one semiconductor wafer is obtained. To reproduce the same conditions as those when processing the production type wafers, however, the same number of sample wafers as the number of production type wafers that would be processed in the actual production line are processed taking the time normally spent to process 100 wafers.